Glutamine Metabolism Is Required for Collagen Protein Synthesis in Lung Fibroblasts

Idiopathic pulmonary fibrosis (IPF) is characterized by the transforming growth factor (TGF)-β-dependent differentiation of lung fibroblasts into myofibroblasts, leading to excessive deposition of extracellular matrix proteins, which distort lung architecture and function. Metabolic reprogramming in myofibroblasts is emerging as an important mechanism in the pathogenesis of IPF, and recent evidence suggests that glutamine metabolism is required in myofibroblasts, although the exact role of glutamine in myofibroblasts is unclear. In the present study, we demonstrate that glutamine and its conversion to glutamate by glutaminase are required for TGF-β-induced collagen protein production in lung fibroblasts. We found that metabolism of glutamate to α-ketoglutarate by glutamate dehydrogenase or the glutamate-pyruvate or glutamate-oxaloacetate transaminases is not required for collagen protein production. Instead, we discovered that the glutamate-consuming enzymes phosphoserine aminotransferase 1 (PSAT1) and aldehyde dehydrogenase 18A1 (ALDH18A1)/Δ¹-pyrroline-5-carboxylate synthetase (P5CS) are required for collagen protein production by lung fibroblasts. PSAT1 is required for de novo glycine production, whereas ALDH18A1/P5CS is required for de novo proline production. Consistent with this, we found that TGF-β treatment increased cellular concentrations of glycine and proline in lung fibroblasts. Our results suggest that glutamine metabolism is required to promote amino acid biosynthesis and not to provide intermediates such as α-ketoglutarate for oxidation in mitochondria. In support of this, we found that inhibition of glutaminolysis has no effect on cellular oxygen consumption and that knockdown of oxoglutarate dehydrogenase has no effect on the ability of fibroblasts to produce collagen protein. Our results suggest that amino acid biosynthesis pathways may represent novel therapeutic targets for treatment of fibrotic diseases, including IPF.

Endogenous itaconate is not required for particulate matter-induced NRF2 expression or inflammatory response

Particulate matter (PM) air pollution causes cardiopulmonary mortality via macrophage-driven lung inflammation; however, the mechanisms are incompletely understood. RNA-sequencing demonstrated Acod1 (Aconitate decarboxylase 1) as one of the top genes induced by PM in macrophages. Acod1 encodes a mitochondrial enzyme that produces itaconate, which has been shown to exert anti-inflammatory effects via NRF2 after LPS. Here, we demonstrate that PM induces Acod1 and itaconate, which reduced mitochondrial respiration via complex II inhibition. Using Acod1^-/- mice, we found that Acod1/endogenous itaconate does not affect PM-induced inflammation or NRF2 activation in macrophages in vitro or in vivo. In contrast, exogenous cell permeable itaconate, 4-octyl itaconate (OI) attenuated PM-induced inflammation in macrophages. OI was sufficient to activate NRF2 in macrophages; however, NRF2 was not required for the anti-inflammatory effects of OI. We conclude that the effects of itaconate production on inflammation are stimulus-dependent, and that there are important differences between endogenous and exogenously-applied itaconate.

Suppression of Superoxide-Hydrogen Peroxide Production at Site IQ of Mitochondrial Complex I Attenuates Myocardial Stunning and Improves Postcardiac Arrest Outcomes

OBJECTIVES

Cardiogenic shock following cardiopulmonary resuscitation for sudden cardiac arrest is common, occurring even in the absence of acute coronary artery occlusion, and contributes to high rates of postcardiopulmonary resuscitation mortality. The pathophysiology of this shock is unclear, and effective therapies for improving clinical outcomes are lacking.

DESIGN

Laboratory investigation.

SETTING

University laboratory.

SUBJECTS

C57BL/6 adult female mice.

INTERVENTIONS

Anesthetized and ventilated adult female C57BL/6 wild-type mice underwent a 4, 8, 12, or 16-minute potassium chloride-induced cardiac arrest followed by 90 seconds of cardiopulmonary resuscitation. Mice were then blindly randomized to a single IV injection of vehicle (phosphate-buffered saline) or suppressor of site IQ electron leak, an inhibitor of superoxide production by complex I of the mitochondrial electron transport chain. Suppressor of site IQ electron leak and vehicle were administered during cardiopulmonary resuscitation.

MEASUREMENTS AND MAIN RESULTS

Using a murine model of asystolic cardiac arrest, we discovered that duration of cardiac arrest prior to cardiopulmonary resuscitation determined postresuscitation success rates, degree of neurologic injury, and severity of myocardial dysfunction. Post-cardiopulmonary resuscitation cardiac dysfunction was not associated with myocardial necrosis, apoptosis, inflammation, or mitochondrial permeability transition pore opening. Furthermore, left ventricular function recovered within 72 hours of cardiopulmonary resuscitation, indicative of myocardial stunning. Postcardiopulmonary resuscitation, the myocardium exhibited increased reactive oxygen species and evidence of mitochondrial injury, specifically reperfusion-induced reactive oxygen species generation at electron transport chain complex I. Suppressor of site IQ electron leak, which inhibits complex I-dependent reactive oxygen species generation by suppression of site IQ electron leak, decreased myocardial reactive oxygen species generation and improved postcardiopulmonary resuscitation myocardial function, neurologic outcomes, and survival.

CONCLUSIONS

The severity of cardiogenic shock following asystolic cardiac arrest is dependent on the length of cardiac arrest prior to cardiopulmonary resuscitation and is mediated by myocardial stunning resulting from mitochondrial electron transport chain complex I dysfunction. A novel pharmacologic agent targeting this mechanism, suppressor of site IQ electron leak, represents a potential, practical therapy for improving sudden cardiac arrest resuscitation outcomes.

Tissue-Resident Alveolar Macrophages Do Not Rely on Glycolysis for LPS-induced Inflammation

Macrophage effector function is dynamic in nature and largely dependent on not only the type of immunological challenge but also the tissue-specific environment and developmental origin of a given macrophage population. Recent research has highlighted the importance of glycolytic metabolism in the regulation of effector function as a common feature associated with macrophage activation. Yet, most research has used macrophage cell lines and bone marrow-derived macrophages, which do not account for the diversity of macrophage populations and the role of tissue specificity in macrophage immunometabolism. Tissue-resident alveolar macrophages (TR-AMs) reside in an environment characterized by remarkably low glucose concentrations, making glycolysis-linked immunometabolism an inefficient and unlikely means of immune activation. In this study, we show that TR-AMs rely on oxidative phosphorylation to meet their energy demands and maintain extremely low levels of glycolysis under steady-state conditions. Unlike bone marrow-derived macrophages, TR-AMs did not experience enhanced glycolysis in response to LPS, and glycolytic inhibition had no effect on their proinflammatory cytokine production. Hypoxia-inducible factor 1α stabilization promoted glycolysis in TR-AMs and shifted energy production away from oxidative metabolism at baseline, but it was not sufficient for TR-AMs to mount further increases in glycolysis or enhance immune function in response to LPS. Importantly, we confirmed these findings in an in vivo influenza model in which infiltrating macrophages had significantly higher glycolytic and proinflammatory gene expression than TR-AMs. These findings demonstrate that glycolysis is dispensable for macrophage effector function in TR-AM and highlight the importance of macrophage tissue origin (tissue resident vs. recruited) in immunometabolism.

Abstract 282: Mitochondrial Complex I Induced Myocardial Stunning Following Cardiopulmonary Resuscitation

Background: Cardiogenic shock following cardiopulmonary resuscitation (CPR) for sudden cardiac arrest is common, occurring even in the absence of acute coronary artery occlusion, and contributes to high rates of post-CPR mortality. The pathophysiology of this shock is unclear and effective therapies for improving clinical outcomes are lacking.

Methods and Results: Using a murine model of asystolic cardiac arrest, we investigated the pathophysiology of post-CPR cardiogenic shock and discovered that duration of cardiac arrest (4, 8, 12 or 16-minute) prior to CPR determined post-resuscitation success rates, degree of neurological injury, and severity of myocardial dysfunction. Post-CPR cardiac dysfunction was not associated with myocardial necrosis, apoptosis, inflammation, or mitochondrial permeability transition pore opening and recovered within several days, indicative of myocardial stunning. Post-CPR myocardial stunning was associated with increases in ventricular and mitochondrial reactive oxygen species (ROS, P <0.001 vs Sham, respectively). Seahorse micropolarimetry of isolated post-CPR cardiac mitochondria revealed decreased rates of maximal oxygen consumption rates (OCR) for both Complex I and Complex II vs controls ( P <0.01 vs Sham, respectively), indicating inhibition of mitochondrial oxidative phosphorylation. Paradoxically, in the presence of ADP stimulated coupled respiration, post-CRP mitochondria demonstrated increased OCR ( P <0.05 vs Sham) and increased rates of proton leak ( P <0.05 vs Sham), suggesting Complex I as the site of ROS generation. These findings were not observed at complex II. S1QEL, a complex I-specific superoxide inhibitor, administered during CPR, decreased myocardial ROS generation while improving post-CPR myocardial function ( P <0.01 vs CPR control), neurological injury ( P <0.01 vs CPR control), and survival ( P <0.01 vs CPR control).

Conclusions: Our results demonstrate that cardiogenic shock following resuscitation from cardiac arrest is consistent with myocardial stunning mediated by mitochondrial complex I injury and ROS generation. Targeting this mechanism represents a novel and practical therapy for improving sudden cardiac arrest resuscitation outcomes.

Anti-fibrotic effects of tannic acid through regulation of a sustained TGF-beta receptor signaling

Background

Pulmonary fibrosis is a progressive disease characterized by structural distortion of the lungs. Transforming growth factor-beta (TGF-beta) is a key cytokine implicated in the pathogenesis of pulmonary fibrosis. TGF-beta-induced myofibroblast differentiation characterized by expression of smooth muscle alpha-actin and extracellular matrix proteins is a key process in pathogenesis of fibrotic disease. Tannic acid is a natural polyphenol with diverse applications. In this study, we investigated the effect of tannic acid on myofibroblast differentiation and pulmonary fibrosis in cultured cells and in bleomycin model of the disease.

Methods

Primary cultured human lung fibroblasts (HLF) were used. The relative levels of proteins were determined by Western blotting. HLF contraction was measured by traction microscopy. Bleomycin-induced pulmonary fibrosis in mice was used as the disease model.

Results

Tannic acid inhibited TGF-beta-induced expression of collagen-1 and smooth muscle alpha-actin (SMA) as well as force generation by HLF. Tannic acid did not affect initial phosphorylation of Smad2 in response to TGF-beta, but significantly inhibited sustained Smad2 phosphorylation, which we recently described to be critical for TGF-beta-induced myofibroblast differentiation. Accordingly, tannic acid inhibited Smad-dependent gene transcription in response to TGF-beta, as assessed using luciferase reporter for the activity of Smad-binding elements. Finally, in mouse model of bleomycin-induced pulmonary fibrosis, therapeutic application of tannic acid resulted in a significant reduction of lung fibrosis, decrease in collagen-1 content and of Smad2 phosphorylation in the lungs.

Conclusions

This study demonstrates the anti-fibrotic effect of tannic acid in vitro and in vivo through a regulation of sustained Smad2 phosphorylation.

Electronic supplementary material

The online version of this article (10.1186/s12931-019-1141-8) contains supplementary material, which is available to authorized users.

Single-Cell Transcriptomic Analysis of Human Lung Provides Insights into the Pathobiology of Pulmonary Fibrosis

Rationale: The contributions of diverse cell populations in the human lung to pulmonary fibrosis pathogenesis are poorly understood. Single-cell RNA sequencing can reveal changes within individual cell populations during pulmonary fibrosis that are important for disease pathogenesis. Objectives: To determine whether single-cell RNA sequencing can reveal disease-related heterogeneity within alveolar macrophages, epithelial cells, or other cell types in lung tissue from subjects with pulmonary fibrosis compared with control subjects. Methods: We performed single-cell RNA sequencing on lung tissue obtained from eight transplant donors and eight recipients with pulmonary fibrosis and on one bronchoscopic cryobiospy sample from a patient with idiopathic pulmonary fibrosis. We validated these data using in situ RNA hybridization, immunohistochemistry, and bulk RNA-sequencing on flow-sorted cells from 22 additional subjects. Measurements and Main Results: We identified a distinct, novel population of profibrotic alveolar macrophages exclusively in patients with fibrosis. Within epithelial cells, the expression of genes involved in Wnt secretion and response was restricted to nonoverlapping cells. We identified rare cell populations including airway stem cells and senescent cells emerging during pulmonary fibrosis. We developed a web-based tool to explore these data. Conclusions: We generated a single-cell atlas of pulmonary fibrosis. Using this atlas, we demonstrated heterogeneity within alveolar macrophages and epithelial cells from subjects with pulmonary fibrosis. These results support the feasibility of discovery-based approaches using next-generation sequencing technologies to identify signaling pathways for targeting in the development of personalized therapies for patients with pulmonary fibrosis.

Metformin Targets Mitochondrial Electron Transport to Reduce Air-Pollution-Induced Thrombosis

Urban particulate matter air pollution induces the release of pro-inflammatory cytokines including interleukin-6 (IL-6) from alveolar macrophages, resulting in an increase in thrombosis. Here, we report that metformin provides protection in this murine model. Treatment of mice with metformin or exposure of murine or human alveolar macrophages to metformin prevented the particulate matter-induced generation of complex III mitochondrial reactive oxygen species, which were necessary for the opening of calcium release-activated channels (CRAC) and release of IL-6. Targeted genetic deletion of electron transport or CRAC channels in alveolar macrophages in mice prevented particulate matter-induced acceleration of arterial thrombosis. These findings suggest metformin as a potential therapy to prevent some of the premature deaths attributable to air pollution exposure worldwide.

Particulate Matter Air Pollution: Effects on the Cardiovascular System

Air pollution is a complex mixture of gaseous and particulate components, each of which has detrimental effects on human health. While the composition of air pollution varies greatly depending on the source, studies from across the world have consistently shown that air pollution is an important modifiable risk factor for significantly increased morbidity and mortality. Moreover, clinical studies have generally shown a greater impact of particulate matter (PM) air pollution on health than the gaseous components. PM has wide-ranging deleterious effects on human health, particularly on the cardiovascular system. Both acute and chronic exposure to PM air pollution is associated with increased risk of death from cardiovascular diseases including ischemic heart disease, heart failure, and ischemic/thrombotic stroke. Particulate matter has also been shown to be an important endocrine disrupter, contributing to the development of metabolic diseases such as obesity and diabetes mellitus, which themselves are risk factors for cardiovascular disease. While the epidemiological evidence for the deleterious effects of PM air pollution on health is increasingly accepted, newer studies are shedding light on the mechanisms by which PM exerts its toxic effects. A greater understanding of how PM exerts toxic effects on human health is required in order to prevent and minimize the deleterious health effects of this ubiquitous environmental hazard. Air pollution is a growing public health problem and mortality due to air pollution is expected to double by 2050. Here, we review the epidemiological evidence for the cardiovascular effects of PM exposure and discuss current understanding about the biological mechanisms, by which PM exerts toxic effects on cardiovascular system to induce cardiovascular disease.

Inhalational exposure to particulate matter air pollution alters the composition of the gut microbiome

Recent studies suggest an association between particulate matter (PM) air pollution and gastrointestinal (GI) disease. In addition to direct deposition, PM can be indirectly deposited in oropharynx via mucociliary clearance and upon swallowing of saliva and mucus. Within the GI tract, PM may alter the GI epithelium and gut microbiome. Our goal was to determine the effect of PM on gut microbiota in a murine model of PM exposure via inhalation. C57BL/6 mice were exposed via inhalation to either concentrated ambient particles or filtered air for 8-h per day, 5-days a week, for a total of 3-weeks. At exposure's end, GI tract tissues and feces were harvested, and gut microbiota was analyzed. Alpha-diversity was modestly altered with increased richness in PM-exposed mice compared to air-exposed mice in some parts of the GI tract. Most importantly, PM-induced alterations in the microbiota were very apparent in beta-diversity comparisons throughout the GI tract and appeared to increase from the proximal to distal parts. Changes in some genera suggest that distinct bacteria may have the capacity to bloom with PM exposure. Exposure to PM alters the microbiota throughout the GI tract which maybe a potential mechanism that explains PM induced inflammation in the GI tract.

Inhibition of Phosphoglycerate Dehydrogenase Attenuates Bleomycin-induced Pulmonary Fibrosis

Organ fibrosis, including idiopathic pulmonary fibrosis, is associated with significant morbidity and mortality. Because currently available therapies have limited effect, there is a need to better understand the mechanisms by which organ fibrosis occurs. We have recently reported that transforming growth factor (TGF)-β, a key cytokine that promotes fibrogenesis, induces the expression of the enzymes of the de novo serine and glycine synthesis pathway in human lung fibroblasts, and that phosphoglycerate dehydrogenase (PHGDH; the first and rate-limiting enzyme of the pathway) is required to promote collagen protein synthesis downstream of TGF-β. In this study, we investigated whether inhibition of de novo serine and glycine synthesis attenuates lung fibrosis in vivo. We found that TGF-β induces mRNA and protein expression of PHGDH in murine fibroblasts. Similarly, intratracheal administration of bleomycin resulted in increased expression of PHGDH in mouse lungs, localized to fibrotic regions. Using a newly developed small molecule inhibitor of PHGDH (NCT-503), we tested whether pharmacologic inhibition of PHGDH could inhibit fibrogenesis both in vitro and in vivo. Treatment of murine and human lung fibroblasts with NCT-503 decreased TGF-β-induced collagen protein synthesis. Mice treated with the PHGDH inhibitor beginning 7 days after intratracheal instillation of bleomycin had attenuation of lung fibrosis. These results indicate that the de novo serine and glycine synthesis pathway is necessary for TGF-β-induced collagen synthesis and bleomycin-induced pulmonary fibrosis. PHGDH and other enzymes in the de novo serine and glycine synthesis pathway may be a therapeutic target for treatment of fibrotic diseases, including idiopathic pulmonary fibrosis.

Experimental Lung Injury Reduces Krüppel-like Factor 2 to Increase Endothelial Permeability via Regulation of RAPGEF3-Rac1 Signaling

RATIONALE

Acute respiratory distress syndrome (ARDS) is caused by widespread endothelial barrier disruption and uncontrolled cytokine storm. Genome-wide association studies (GWAS) have linked multiple genes to ARDS. Although mechanosensitive transcription factor Krüppel-like factor 2 (KLF2) is a major regulator of endothelial function, its role in regulating pulmonary vascular integrity in lung injury and ARDS-associated GWAS genes remains poorly understood.

OBJECTIVES

To examine KLF2 expression in multiple animal models of acute lung injury and further elucidate the KLF2-mediated pathways involved in endothelial barrier disruption and cytokine storm in experimental lung injury.

METHODS

Animal and in vitro models of acute lung injury were used to characterize KLF2 expression and its downstream effects responding to influenza A virus (A/WSN/33 [H1N1]), tumor necrosis factor-α, LPS, mechanical stretch/ventilation, or microvascular flow. KLF2 manipulation, permeability measurements, small GTPase activity, luciferase assays, chromatin immunoprecipitation assays, and network analyses were used to determine the mechanistic roles of KLF2 in regulating endothelial monolayer integrity, ARDS-associated GWAS genes, and lung pathophysiology.

MEASUREMENTS AND MAIN RESULTS

KLF2 is significantly reduced in several animal models of acute lung injury. Microvascular endothelial KLF2 is significantly induced by capillary flow but reduced by pathologic cyclic stretch and inflammatory stimuli. KLF2 is a novel activator of small GTPase Ras-related C3 botulinum toxin substrate 1 by transcriptionally controlling Rap guanine nucleotide exchange factor 3/exchange factor directly activated by cyclic adenosine monophosphate, which maintains vascular integrity. KLF2 regulates multiple ARDS GWAS genes related to cytokine storm, oxidation, and coagulation in lung microvascular endothelium. KLF2 overexpression ameliorates LPS-induced lung injury in mice.

CONCLUSIONS

Disruption of endothelial KLF2 results in dysregulation of lung microvascular homeostasis and contributes to lung pathology in ARDS.

Monocyte-derived alveolar macrophages drive lung fibrosis and persist in the lung over the life span

Misharin et al. elucidate the fate and function of monocyte-derived alveolar macrophages during the course of pulmonary fibrosis. These cells persisted throughout the life span, were enriched for the expression of profibrotic genes, and their genetic ablation ameliorated development of pulmonary fibrosis.

Little is known about the relative importance of monocyte and tissue-resident macrophages in the development of lung fibrosis. We show that specific genetic deletion of monocyte-derived alveolar macrophages after their recruitment to the lung ameliorated lung fibrosis, whereas tissue-resident alveolar macrophages did not contribute to fibrosis. Using transcriptomic profiling of flow-sorted cells, we found that monocyte to alveolar macrophage differentiation unfolds continuously over the course of fibrosis and its resolution. During the fibrotic phase, monocyte-derived alveolar macrophages differ significantly from tissue-resident alveolar macrophages in their expression of profibrotic genes. A population of monocyte-derived alveolar macrophages persisted in the lung for one year after the resolution of fibrosis, where they became increasingly similar to tissue-resident alveolar macrophages. Human homologues of profibrotic genes expressed by mouse monocyte-derived alveolar macrophages during fibrosis were up-regulated in human alveolar macrophages from fibrotic compared with normal lungs. Our findings suggest that selectively targeting alveolar macrophage differentiation within the lung may ameliorate fibrosis without the adverse consequences associated with global monocyte or tissue-resident alveolar macrophage depletion.

Prolonged Exposures to Intermittent Hypoxia Promote Visceral White Adipose Tissue Inflammation in a Murine Model of Severe Sleep Apnea: Effect of Normoxic Recovery

Study Objective

Increased visceral white adipose tissue (vWAT) mass results in infiltration of inflammatory macrophages that drive inflammation and insulin resistance. Patients with obstructive sleep apnea (OSA) suffer from increased prevalence of obesity, insulin resistance, and metabolic syndrome. Murine models of intermittent hypoxia (IH) mimicking moderate-severe OSA manifest insulin resistance following short-term IH. We examined in mice the effect of long-term IH on the inflammatory cellular changes within vWAT and the potential effect of normoxic recovery (IH-R).

Methods

Male C57BL/6J mice were subjected to IH for 20 weeks, and a subset was allowed to recover in room air (RA) for 6 or 12 weeks (IH-R). Stromal vascular fraction was isolated from epididymal vWAT and mesenteric vWAT depots, and single-cell suspensions were prepared for flow cytometry analyses, reactive oxygen species (ROS), and metabolic assays.

Results

IH reduced body weight and vWAT mass and IH-R resulted in catch-up weight and vWAT mass. IH-exposed vWAT exhibited increased macrophage counts (ATMs) that were only partially improved in IH-R. IH also caused a proinflammatory shift in ATMs (increased Ly6c(hi)(+) and CD36(+) ATMs). These changes were accompanied by increased vWAT insulin resistance with only partial improvements in IH-R. In addition, ATMs exhibited increased ROS production, altered metabolism, and changes in electron transport chain, which were only partially improved in IH-R.

Conclusion

Prolonged exposures to IH during the sleep period induce pronounced vWAT inflammation and insulin resistance despite concomitant vWAT mass reductions. These changes are only partially reversible after 3 months of normoxic recovery. Thus, long-lasting OSA may preclude complete reversibility of metabolic changes.

HIF-1α is required for disturbed flow-induced metabolic reprogramming in human and porcine vascular endothelium

Hemodynamic forces regulate vascular functions. Disturbed flow (DF) occurs in arterial bifurcations and curvatures, activates endothelial cells (ECs), and results in vascular inflammation and ultimately atherosclerosis. However, how DF alters EC metabolism, and whether resulting metabolic changes induce EC activation, is unknown. Using transcriptomics and bioenergetic analysis, we discovered that DF induces glycolysis and reduces mitochondrial respiratory capacity in human aortic ECs. DF-induced metabolic reprogramming required hypoxia inducible factor-1α (HIF-1α), downstream of NAD(P)H oxidase-4 (NOX4)-derived reactive oxygen species (ROS). HIF-1α increased glycolytic enzymes and pyruvate dehydrogenase kinase-1 (PDK-1), which reduces mitochondrial respiratory capacity. Swine aortic arch endothelia exhibited elevated ROS, NOX4, HIF-1α, and glycolytic enzyme and PDK1 expression, suggesting that DF leads to metabolic reprogramming in vivo. Inhibition of glycolysis reduced inflammation suggesting a causal relationship between flow-induced metabolic changes and EC activation. These findings highlight a previously uncharacterized role for flow-induced metabolic reprogramming and inflammation in ECs.